The present invention relates to a ball valve in which a ball and ball seats are respectively mounted in and formed in a valve body, and also to a method of fabricating such a ball valve.
A conventional ball valve and method of fabrication thereof are disclosed in U.S. Pat. No. 3,807,692. In this ball valve, recessed surfaces are provided at both ends of a flow passage formed in the ball. The recessed surfaces extend inwardly from the spherical surface of the ball. A valve body, which is molded by injection molding, presses the ball seats against the recessed surfaces of the ball. In the closed state of the valve, the ball seats are pressed more strongly against the spherical surface of the ball than in the open state, thereby to obtain a good seal between the ball and the ball seats.
The conventional ball valve described above has ball seats molded such that the ball seats are pressed or deformed against the recessed surfaces of the ball. As a result, the ball seats are acted upon by a deforming force, even in the open state, but with the larger deformation being present in the closed state.
Fluoroplastics, represented by ethylene tetrafluoride which has an excellent resistance to chemical reaction, a high thermal stability and high resistance to wear, have been widely used for ball seats. However, fluoroplastics have a small range of elastic deformation, and therefore the maximum amount of deformation of the ball seats cannot be large. Thus, the maximum amount of pressure acting between the ball and the ball seats is limited in the closed state. Moreover, with this material, the resiliency tends to decrease over a period of time.
If the depth of the recessed surfaces is made large for the purpose of increasing the sealing ability between the ball and the ball seats, an undesirably large torque is required to operate the valve.
Further, during manufacture, there is a large possibility of the ball being misshapen because of the resin pressure which exists when the molten resin is injected into a mold to form the valve body. In such a case, the pressure between the ball and the ball seats on opposite sides of the ball may be different, thereby undesirably causing a loss in sealing ability.
The primary object of the present invention is, in view of the problems in the conventional ball valve, to provide a ball valve which has good sealing, a high durability and a good performance in operation, and in which, in molding, recessed surfaces of the ball do not contact the lips of ball seats.